1. Field of the Invention
The present invention generally relates to a disk carrier device and a disk drive. More particularly, this invention relates to a disk carrier device for carrying an optical disk and a disk drive including the disk carrier device.
2. Description of the Related Art
In recent years, digitization of information has accelerated as seen in the start of digital TV broadcasting and this trend has increased the demand for an optical disk with higher capacity or the demand for recording information at higher density on an optical disk. One way to meet such a demand is to reduce the spot diameter of a laser beam used to record or reproduce information on an optical disk.
The spot diameter of a laser beam can be reduced by using a laser beam with a shorter wavelength or by increasing the numerical aperture (NA) of an objective lens. However, reducing the wavelength of a laser beam or increasing an NA reduces the depth of focus of an optical system including an objective lens and therefore makes it necessary to improve the accuracy of a focus servo. Also, increasing an NA results in a reduced distance between an objective lens and a recording surface of an optical disk and therefore makes it necessary to reduce the out-of-plane motion (deviation of the surface of an optical disk from a plane, or movement of an optical disk in the direction of its rotational axis) of an optical disk, for example, to prevent an optical pickup including an objective lens from contacting the optical disk.
Under the above circumstances, optical disks (may also be called flexible optical disks) made of flexible thin-film sheets with recording surfaces are being developed, and an optical disk drive that rotates a flexible optical disk on a stabilizing plate and thereby effectively reduces the out-of-plane motion of a flexible optical disk has been proposed (see, for example, patent documents 1 and 2). Since the substrate of a flexible optical disk is a fragile thin-film sheet, a rigid hub made of, for example, a metal is normally provided in the center of a flexible optical disk. When a flexible optical disk is taken out of a disk cartridge and mounted on a disk drive, the flexible optical disk is held on a disk carrier device by, for example, attracting its hub with an electromagnet.
However, to hold a flexible optical disk using an electromagnet, it is necessary to continuously supply an exciting current to excite the electromagnet while carrying a flexible optical disk. This increases the electric power needed and the amount of heat generated when carrying a flexible optical disk. Meanwhile, multiple flexible optical disks may be stacked in a disk cartridge to implement a compact, high-capacity data storage. In such a case, it is preferable to make the hub of a flexible optical disk as thin as possible. However, making a hub thinner makes it necessary to increase an exciting current.
[Patent document 1] Japanese Patent Application Publication No. 10-308059
[Patent document 2] Japanese Patent Application Publication No. 2003-115108